Friction reducing additives for lubricants



Patented Sept. 14, 1954 UNITED STATES PATENT OFFICE FRICTION REDUCING ADDITIVES FOE LUBRICANTS a body corporate No Drawing. Application December 16, 1950, Serial No. 201,228

6 Claims. 1

The present invention relates to friction reducing additives for lubricants and, particularly, to additive materials which may be incorporated in lubricating oils and greases to reduce the coeflicient of friction between metallic bearings, especially bearings of the journal type.

The operation of various types of machinery, and particularly of heavy machinery, where starting torques are relatively high, frequently involves starting difficulties and high power consumption. In the past, various materials have been proposed for reducing the coefiicient of friction such as fatty acids and soaps, e. g., of the C8 to C22 fatty series. While the exact mechanism is not clearly understood, it appears that the appreciable reduction in the friction coefficient which is obtained by using such soaps and acids may result from a reaction between metal (or the metal oxide which may cover the metal surface) and the additive to produce a monolayer of metal soap on the surface of the bearing. Such monolayers have excellent low friction characteristics, for sliding friction particularly, but the monolayers also have the disadvantage, apparently, of being removed rapidly, resulting in excessive wear. It seems, in fact, that monolayers of soap tend to be removed and renewed so rapidly that there is a constant metal reaction taking place. On the other hand, when multi-layers of soap in lubricants are utilized to reduce friction, they tend apparently to be selfrepairing under certain operational conditions. If they are incorporated in liquid vehicles they appear to repair themselves without excessive wear under conditions of boundary lubrication, e. g., when bearings of the journal type are operating under high load conditions at relatively low velocities.

The ordinary soaps and fatty acids used in greases, gear oils, and the like, commonly react with the bearing metals to produce metallic compounds which are oil-soluble. In the presence ,of lubricating oil, they appear to be susceptible to washing away from the metal surface. Where air or oxygen is present, and particularly in the presence of moisture and heat, this process of metal salt or soap formation and solution progresses rapidly. As a result, the metallic bearing materials may be corroded or dissolved quite rapidly under conditions of high load, especially in the presence of moisture, heat and oxygen or air. Particularly in heavy machinery of the type used in paper mills operating under heavy loads in direct contact with steam and/or water, corrosion of bearings and journals progresses at a rapid rate. On important object of the present invention, therefore, is to overcome such wear and corrosion.

According to the present invention, polymeric materials comprising fatty acids of a type having at least moderate solubility in lubricating oils but forming with bearing metals, relatively oil-insoluble products, in the form of metalloorganic complexes containing polymeric materials, may be used to overcome the difiiculties mentioned above.

where any of the radicals R is an aliphatic hydrocarbon chain of at least 8 carbon atoms and may be as high as about 22 carbon atoms. The latter material may be derived in a manner similar to that used for producing acrylic acid or polyacrylic acid, being synthesized as follows:

which polymerizes to Since neither of the foregoing compounds is available commercially at the present time, it has been found according to the present invention that certain resinous or polymeric materials of the alkyd or so-called glyptal type derived from glycerine and phthalic anhydride, which contain acidic constituents and which may readily be prepared or are readily available on the market, may be used in lieu of those represented in the above formulas. It is preferred that these materials be soluble in oil, at least in the proportions employed, and preferably in proportions up to 5% by weight or a little higher. Also, the reaction products of polybasic acids, or their anhydrides, with polyhydric alcohols may be used, the product being modified by treatment with Acids of the general formula fatty acid, produces resinous additive materials having the characteristics desired. Reaction products such as those of the general formula where n is a small integer preferably between 1 and =8, and m is an integer of such value as to make an oil-soluble resin product may be prepared by known methods. As previously indicated, the metal-containing reaction or chemisorption product of this additive, formed by contact with the bearing metal, tends to be quite oil-insoluble.

Where the polybasic acid constituent of the resin or other polymer is of aromatic type, such as phthalic acid, the above product may be represented, so far as its acidic component is concerned, by the general formula O 4) I m having a value, as indicated above, such that the resin itself is oil-soluble but its reaction or chemi-sorption product, salt or the like, formed with the bearing metal, is relatively oil-insoluble. The anhydrides of the dibasic acids are preferred over the acids themselves because they react more readily though either can be used.

Specifically, compounds of the type described in the last two formulas above have been prepared by condensing glycerol and stearic or behenic acids with phthalic, succinic or maleic anhydrides. The modified alkyd resins are preferred, although the related acrylic resins, simi larly modified, may be used, as suggested above.

Alternatively, the glycerol monostearate or the corresponding behenic acid partial ester of glycerol may be condensed with any of the above anhydrides. These resinous or polymeric derivatives may be added to lubricating oils and greases i in proportions of 0.01 to l or 2% by weight, based on the total composition. Proportions of 0.1 to about 1.0%, especially about 0.2 to 0.5%, are specifically preferred.

In carrying out the invention, condensates prepared according to the preceding paragraph were added to mineral base lubricating oil in various concentrations. The starting friction and the running friction in relatively heavy bearing journals were measured at very low sliding velocities, e. g., about 12 inches per minute. With very small concentrations of additive the friction coefficient dropped off rapidly as the concentration of the acid-containing resin in the oil was increased up to about 0.5% by weight, based on the total lubricant. Above 0.5% concentration, the friction coefiicient levelled out.

The acid-containing additives preferably have a moderately low acid number when that number represents available acid. However, these resinous materials may contain a substantial proportion of acid which is tied up in the polymer. Modified acrylic resins may be used. Free fatty acids, in any substantial quantities, are corrosive and are to be avoided, but acids having free carboxyl groups, which otherwise are tied up in the polymer, are very satisfactory.

EXAMPLE I A resin was prepared by condensing 74 grams of phthalic anhydride with 4.6 grams of glycerol and 142 grams of technical stearic acid. The finished condensation product had an acid number of 7.4 and was a dark brown resinous material solid at room temperature.

EXAMPLE II A product was prepared in much the same manner as Example I, using '74 grams of phthalic anhydride, 50 grams of glycerol and 142 grams of stearic acid, technical grade. This product had an acid number of 9.0 and was also a dark brown solid resinous material at room temperature.

In lieu of the anhydride it is possible, of course, to use the corresponding acid.

EXAMPLE III A composition was prepared by condensing 23.2 grams of maleic acid with 71.6 grams of glycerol monostearate. This produce which had an acid number of 18.0 was a yellowish solid at room temperature. It was partially soluble in mineral lubricating oil of 300 S. S. U. viscosity at F. The mineral oil had a viscosity index of 54. When the oil was heated to C. there was no insoluble residue even when the resin was used in 5% concentration by weight.

EXAMPLE IV Another composition was prepared of 10.0 grams succinic anhydride, 9.2 grams glycerol and 34.5 grams behenic acid. This product had an acid number of 100.0 and was also a solid resinous material with moderate solubility in mineral lubricating oil.

All four of the resins produced according to the foregoing examples were dissolved in a mineral base lubricating oil of about 300 S. S. U. viscosity at 100 F. (54 viscosity index), by heating the oil and resin mixture to a temperature of C. Thereafter, the lubricants were cooled to room temperature and were centrifuged in order to separate any oil-insoluble portions. In the case of Example III, appreciable quantities of the 5% solution were separated but the quantities separated were negligible in the other examples.

In order to be certain that the reduction of friction which was found was not due entirely to an increase in viscosity of the resin-oil solution, viscometric measurements were take on several samples of various concentrations with results as indicated in Table I:

Table I VISCOSITY or OILS AND ADDITIVES 100 F.)

Viscosity Alkyd Solution by Weight of Solution (S. S. U.)

Example I 5% 1111300 viscosity S. S. U. 54 V. I. l

oi 333 Do l0%1,1in 300 viscosity S. S. U. 54 V. l. 375

o Example II 5%iiln 300 viscosity S. S. U. 54 V. I 334 o Do 10% in 300 viscosity 5. S. U. 54 V. I. 382

01 Example III 5%iiln 300 viscosity S. S. U. 54 V. I. 307

o Base Oil Qnly. 300 viscosity S. S. U. 54 V. I. oil W 295 Mmeral 011 Only. 900 viscosity S. S. U. 40 V. I. oil 900 It will be noted in Table I that a mineral lubricating oil of 900 S. S. U. viscosity and viscosity lliitlllllll\lllWllllllllllllWWWW w index of 40 was compared with the base oil and also with the base oil containing various proportions of the additives. Friction measurements also were compared with the oil of 900 S. S. U. viscosity and with the base oil of 300 S. S. U. viscosity (at 100 F.), using steel journals against bearings of Babbitt, steel and Phosphor bronze, respectively. Plastic bearings 01" Teflon and of polythene were used with the steel journals.

Example III resin had a much higher acid number than Examples I and II though not so high as Example IV.

In general, the invention contemplates the use of proportions from 0.1 to as much as 5% of the oil-soluble modified or acid-containing resins which form oil-insoluble complexes with the base metals as contained in bearings, previously dis cussed. Conventional anti-oxidants, oiliness For comparative purposes, the same 11 of 300 agents, extreme pressure additives and viscosity S. S. U. viscosity and 54 viscosity index was used index improvers may be added without departing throughout as the vehicle for the resinous acidfrom the spirit of the invention. The additives containing additive and for the other additives are particularly suited for use in mineral base listed. Results of the friction coefficient tests lubricating oils but they may also be incorporated are summarized in Table II. in synthetic oils such as the dibasic acid esters,

Table II OOEFFICENT OF SLIDING FRICTION FOR VARIOUS LUBRICATING SYSTEMS Phosphor Additive Description g gt Steel, 0. FJ B601%\ZG,

900 visc. V. I. Lubricating mineral oil 0.423 0.447 0.433

300 Visc. 54 V. I. Lubricating mineral oil 0.501 0.521 0.417

5% solution in 300 7180. 54 V. I. oil 0.329 0. 339 0.342

10% solution+0.6% Ca(0H)z in 300 Visc. 54 V. I. oil 0. 236 0. 299 0.305

1% in 300 Visc. 54 V. I. 011 A 0.295 0. 339 0. 300

5% in 300 Visc. 54 V. I. oil A 0. 531 0. 610 0. 447

10% in 300 Visc. 54 V. I. oil .A 0.551 0. 595 O. 422

Rubbed against Babbitt H 0.270

As above, in presence of oil 0. 221

2% dispersion in oil, blended by means of Waring 0. 303 0.393 0.388

Blender.

5% in 300 Visc. 54 V. I. 011 B 0. 467 0. 427 0. 403

Oil 0 200 S. S. U. viscosity 0.496 0.575 0.393

Example III 5% Maleic-glycerol monostearate in Oil 0.221 0. 280 0. 289

Calcium Stearate. 1% dissolved by heat in 300 Visc. 54 V. I. oil 0 0.265 0.383 0.339

0 1% dispersion in Waring Blendor+oil 0.305

Example III 5% Maleic-glycerol monostearate 0.275 0. 295 0.299

0 0.2% Maleic-glycerol monostearat 0. 290 0.319 0.339

Do 0.02% Maleic-glycerol monostearate 0. 359 0. 373 0.373

Example IV Behenic-glycerol-succmic anhydride 2% 0.184 0.314 0. 319

Behenic Acid 2%. Not very soluble in oil at room temperat 0 334 O. 314 0.275

Steel-Teflon Bearing No oil, 0. F. =0.113

Polythene Bearing No oil, C. F. =0.

DO -|oil, C, F. =O.369

1 Coellicient of friction.

2 Ca(OI-I)z used here to completely neutralize any acid.

It should be noted that the coefiicients of friction set forth in the foregoing table are relative and not absolute. The so-called coefficient here is actually a measure of two variables, via, of interference between rugosities, which depends on the finish of the bearings, and of the tendency of two contacting metal surfaces to adhere and oils of the polyglycol or glycol ether type, used alone or in mixtures with each other, and/ or mineral base lubricants. The friction reducing agents of the present invention may also be used in lubricating greases with beneficial results of the same order.

It will be noted in reference to Table II that or weld together. the average bearing metals lubricated with Copper corrosion tests were conducted by placstraight mineral lubricating oil have sliding fricing mechanically polished copper strips in varition coemcients in the neighborhood of ous solutions of the respective examples as fol- With the additives of the present invention, these lows: coeflicients drop to the order of 0.300, being a low as 0.184 in one case. This very substantial (a) 33 amd m a medmm grade lubn' reduction in sliding friction is of considerable (b) 2% of maleic acid-glycerol monostearate vahie m the lubfqwatlon 9 lalge 30mm? P i resin (Example III) of acid number 18in the as m paper mills and n heavy mammmy same on other types where starting torques frequently (6) oil withbut additive 6O impose extremely heavy loads on electric drivlng (d) 0 187 qtearip motors. Reduction in overload starting is par- 0 and m mmeral O11 (eqmva t larl useful Savin in power consumpt on lent to acid number of 6). These were heaty g ed at 100 C for 20 hours in an air oven mm eover Is very conslderable' Another aspect of the present invention in- Copper tests showed that the stearic acid had volves the use of the resinous modifiers, and rea distinct green discoloration after 4 hours at lated materials, to inhibit oxidation of the lubri- 100 C. and this color increased in intensity with cant. Resins prepared by condensing glycerol time. The product of Example III showed no partial esters of long chain fatty acids (C16 to C22) noticeable copper corrosion. The solution ((1) with phthalic, succinic, itaconic, maleic and containing 0.18% of stearic acid was tested to other closely homologous and analogous polydetermine whether copper corrosion is directly basic acids and anhydrides have been found to proportional to acid number. It was found that be effective agents for preventing discoloration the stearic'acid was substantially more corrosive of lubricating oils and greases. to copper, even in the low concentration of 0.18%, When hydrocarbon oils and greases are heated in the presence of air, they tend to absorb oxygen.

than the resin of Example III. As noted above,

Their viscosities increase and they harden and produce sludge in varying degrees, depending upon their chemical stability. The rate of darkening may, in many cases, be taken as a measure of the rate of oxidation. Certain of the condensation products of polybasic acids and long chain substituted polyhydric alcohols are found to reduce the rate of darkening very appreciably. The resinous condensation products must be oil-soluble and their action appears to be rather specific. The following data show changes in light transmission and viscosity after 40 cc. samples of the materials indicated were heated in open beakers for 24 hours at 300 F. All additives were used in 1% concentration. The base oil was a refined lubricating oil of about 300 S. S. U. viscosity at 100 F. and a viscosity index of 95.

The resin was prepared by condensing equimolar proportions of maleic acid and glycerol monostearate. This resin had an acid number of 18.

From the foregoing, it appears that these modified alkyd type resins have several advantageous properties. They may be used in lubricants (1) To waterproof the silica in silica base greases.

(2) Act as friction reducing ingredients in oils and greases generally.

(3) Inhibit oxidation in lubricants and greases generally.

For purposes of preventing oxidation, the modified resins may be used in proportions of 0.1 to 2% or more, based on the total weight of the composition. Proportions of 0.5 to 1% are spe- I cifically preferred.

What is claimed is:

1. A lubricating composition for heavy journal aetallic bearings operating at elevated temperatures in the presence of moisture, comprising a mineral oil base lubricant containing 0.1 to about 1 by weight, based on the total composition, of a fatty acid modified resin selected from the group consisting of the condensation products of glycerol with a dicarboxylic acid material selected from the group consisting of phthalic, succinic and maleic acids and their anhydrides modified by treatment with long chain fatty acids having about 12-22 carbon atoms, and the condensation products of C12-C22 long chain fatty acid esters of glycerol with said dicarboxylic acid materials, said resin having free acidity to the extent of an acid number of about 7-100 and having suinciently active carboxylic groups to form substantially oil-insoluble chemi-sorption products with the metal of said bearings at the operating temperature, said resin being substantially devoid of free fatty acid which would form oil-soluble soap with said metal.

2. A lubricating composition comprising a major proportion of mineral base lubricating oil and 0.1 to 1%, based on the weight of the total composition, of an oil-soluble resinous condensation product of glycerol and phthalic anhydride modified by treatment with a fatty acid of the C12 to C22 range to bring the acid number between about 7.4 and 9.0, said resin being of such molecular weight that the metal soaps thereof are substantially oil-insoluble.

3. Composition according to claim 2 containing about 0.2 to 0.5% of said modified resin.

1. A lubricating composition comprising a major proportion of mineral base lubricating oil and a minor but oxidation inhibiting proportion of about 0.1-1% by weight of the resinous condensation product of C12-C22 long chain fatty acid partial esters of glycerol with a dibasic acidic material selected from the group which consists of phthalic, succinic, and maleic acid and their anhydrides, said condensation product having an acid number of about 7-10 anhydrides.

5. A composition comprising a major propor tion of mineral base lubricating oil and 0.1 to 1% by weight of the resinous condensation pro-dnet of glycerol monostearate and maleic acid.

6. Composition according to claim 5 containing 0.5 to 1% of said condensation product.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,104,408 Wiezevich Jan. 4, 1938 2,201,217 Ballard May 21, 1940 FOREIGN PATENTS Number Country Date 470,580 Great Britain Aug. 18, 1937 OTHER REFERENCES Natl Petroleum News, November 16, 1938, p. R-568. 

1. A LUBRICATING COMPOSITION FOR HEAVY JOURNAL METALLIC BEARINGS OPERATING AT ELEVATED TEMPERATURES IN THE PRESENCE OF MOISTURE, COMPRISING A MINERAL OIL BASE LUBRICANT CONTAINING 0.1 TO ABOUT 1% BY WEIGHT, BASED ON THE TOTAL COMPOSITION, OF A FATTY ACID MODIFIED RESIN SELECTED FROM THE GROUP CONSISTING OF THE CONDENSATION PRODUCTS OF GLYCEROL WITH A DICARBOXYLIC ACID MATERIAL SELECTED FROM THE GROUP CONSISTING OF PHTHALIC, SUCCINIC AND MALEIC ACIDS AND THEIR ANHYDRIDES MODIFIED BY TREATMENT WITH LONG CHAIN FATTY ACIDS HAVING ABOUT 12-22 CARBON ATOMS, AND THE CONDENSATION PRODUCTS OF C12-C22 LONG CHAIN FATTY ACID ESTERS OF GLYCEROL WITH SAID DICARBOXYLIC ACID MATERIALS, SAID RESIN HAVING FREE ACIDITY TO THE EXTENT OF AN ACID NUMBER OF ABOUT 7-100 AND HAVING SUFFICIENTLY ACTIVE CARBOXYLIC GROUPS TO FORM SUBSTANTIALLY OIL-INSOLUBLE CHEMI-SORPTION PRODUCTS WITH THE METAL OF SAID BEARINGS AT THE OPERATING TEMPERATUE, SAID RESIN BEING SUBSTANTIALLY DEVOID OF FREE FATTY ACID WHICH WOULD FORM OIL-SOLUBLE SOAP WITH SAID METAL. 